A. Field of the Invention
The present invention relates to an apparatus and method for initializing an optical recording media. The present invention also relates to an initializing apparatus for changing an amorphous recording layer of an optical disc into a crystal recording layer. The invention may be used to manufacture phase-change optical recording media. The present invention also relates to a system for verifying uniform crystallization of phase-change optical recording media.
B. Description of the Related Art
In optical recording discs with rewrite capability, such as a CD-RW phase-change optical recording disc, a first dielectric layer, a recording layer, a second dielectric layer and a metal layer are formed on a disc substrate. The substrate is generally made of polycarbonate. A UV hardening layer may be provided on the metal layer.
The phase-change recording material of the CD-RW optical disc transitions into either (1) a crystal condition by lengthening the cooling time after it has been heated, or (2) an amorphous condition by shortening the cooling time after it has been melted. Phase-change recording media can record information in the form of marks by reversibly changing between the crystal condition and the amorphous condition. A recording signal can be used to change the intensity of the optical beam that is radiated on the recording layer to change the recording layer from a crystal condition to an amorphous condition, or vice versa. When forming marks, the optical beam intensity may be set at the amorphous level. On non-mark portions, the intensity of the optical beam intensity is set at the crystal level, and the recording layer is crystallized. Since non-mark portions are not heated as much and cool slowly, they transition into the crystal condition regardless of whether they were in an amorphous condition or in a crystal condition.
On the other hand, when manufacturing phase-change recording media, the recording layer is left in an amorphous condition after spattering. Therefore, it is necessary to crystallize all of the recording layer. This crystallization process is called the initialing process. As mentioned above, the length of the cooling time effects the transition to either the crystal condition or the amorphous condition. When the cooling time is longer, the recording layer transitions into the crystal condition. When the cooling time is shorter, the recording layer transitions into the amorphous condition. Therefore, in the initializing process of the recording layer, an optical beam is radiated on the recording layer and the cooling time is made longer after raising the temperature of the recording layer.
Because the substrate is generally made from polycarbonate, it is possible to exceed the heat-resisting properties of the material if the entire surface is initialized simultaneously. The initializing process is generally carried out by radiating an optical beam on the optical recording media while rotating the optical recording media. Successive portions of the recording layer are crystallized as the radiating position is moved in the radial direction.
One problem with the above-described scanning system is that any instability in the optical beam can result in incomplete crystal portions on the recording layer. If there are incomplete crystal portions, problems with recording and reproducing signals are caused, and it is impossible to record and reproduce information accurately.